effectiveness of interventions targeting air travellers for delaying local outbreaks CORD-Papers-2022-06-02 (Version 1)

Title: Effectiveness of interventions targeting air travellers for delaying local outbreaks of SARS-CoV-2
Abstract: Background: We evaluated if interventions aimed at air travellers can delay local SARS-CoV-2 community transmission in a previously unaffected country. Methods: We simulated infected air travellers arriving into countries with no sustained SARS-CoV-2 transmission or other introduction routes from affected regions. We assessed the effectiveness of syndromic screening at departure and/or arrival & traveller sensitisation to the COVID-2019-like symptoms with the aim to trigger rapid self-isolation and reporting on symptom onset to enable contact tracing. We assumed that syndromic screening would reduce the number of infected arrivals and that traveller sensitisation reduces the average number of secondary cases. We use stochastic simulations to account for uncertainty in both arrival and secondary infections rates and present sensitivity analyses on arrival rates of infected travellers and the effectiveness of traveller sensitisation. We report the median expected delay achievable in each scenario and an inner 50% interval. Results: Under baseline assumptions introducing exit and entry screening in combination with traveller sensitisation can delay a local SARS-CoV-2 outbreak by 8 days (50% interval: 3-14 days) when the rate of importation is 1 infected traveller per week at time of introduction. The additional benefit of entry screening is small if exit screening is effective: the combination of only exit screening and traveller sensitisation can delay an outbreak by 7 days (50% interval: 2-13 days). In the absence of screening with less effective sensitisation or a higher rate of importation these delays shrink rapidly to less than 4 days. Conclusion: Syndromic screening and traveller sensitisation in combination may have marginally delayed SARS-CoV-2 outbreaks in unaffected countries.
Published: 2020-02-13
DOI: 10.1101/2020.02.12.20022426
DOI_URL: http://doi.org/10.1101/2020.02.12.20022426
Author Name: Clifford Samuel J
Author link: https://covid19-data.nist.gov/pid/rest/local/author/clifford_samuel_j
Author Name: Pearson Carl A B
Author link: https://covid19-data.nist.gov/pid/rest/local/author/pearson_carl_a_b
Author Name: Klepac Petra
Author link: https://covid19-data.nist.gov/pid/rest/local/author/klepac_petra
Author Name: Van Zandvoort Kevin
Author link: https://covid19-data.nist.gov/pid/rest/local/author/van_zandvoort_kevin
Author Name: Quilty Billy J
Author link: https://covid19-data.nist.gov/pid/rest/local/author/quilty_billy_j
Author Name: Eggo Rosalind M
Author link: https://covid19-data.nist.gov/pid/rest/local/author/eggo_rosalind_m
Author Name: Flasche Stefan
Author link: https://covid19-data.nist.gov/pid/rest/local/author/flasche_stefan
sha: f29dfcd082fe2129574776158dcee28fe7a01cbc
license: medrxiv
source_x: MedRxiv; WHO
source_x_url: https://www.who.int/
url: https://doi.org/10.1101/2020.02.12.20022426
has_full_text: TRUE
Keywords Extracted from Text Content: medRxiv traveller travellers b SARS-CoV-2 c border CIs medRxiv UK air-traveller https://github.com/samclifford/screening_outbreak_delay T 0 patients θ US self-isolate k. Covid-19 border COVID-2019-like air-passengers k=0.16 traveller R eff Air-traveller individuals ܴ participants R=2.5 e er ne k travellers SARS-CoV-2 line λ coronavirus
Extracted Text Content in Record: First 5000 Characters:To determine if interventions aimed at air travellers can delay establishment of a SARS-CoV-2 outbreak in a previously unaffected country with no shared border with China. Methods Summary: Determining how many imported cases are needed to trigger an outbreak in a new location is critical to quantifying if SARS-CoV-2 outbreaks can be delayed. Here we rely on the "outbreak threshold", which is a function of the average number of secondary cases produced by each infected case, plus the variation from person-to-person in how many secondary cases they generate (often referred to as "the dispersion parameter, k"). We define a traveller intervention as either: a) screening for symptoms at either departure or arrival, b) sensitisation of arrivals to signs of illness, or c) a combination of both. We assume that sensitisation will result in a lower individual reproduction number for the traveller (e.g. by self-isolation and more rapid reporting which triggers contact tracing) and that syndromic screening reduces the number of infected travellers who can seed an outbreak. We then calculate the delay in reaching the outbreak threshold according to the number of infected travellers arriving each week, and the effectiveness of interventions a, b, and c, assuming the basic reproduction number to be gamma distributed with CIs ranging from 1.4 to 3.9. Because of the considerable uncertainty in the estimate we report no central estimates but rather 50% and 95% quantiles, focusing specifically on the lower bounds as a measure of likely minimal impact. Results Summary: We evaluated sensitisation effectiveness of 30, 50 and 70%, assuming either 1, 10, or 100 infected travellers per week. We found that early in the outbreak when only few infected travellers arrive, traveller sensitisation can delay a major outbreak in a previously unaffected region. For 50% effectiveness, and assuming 1 infected traveller per week, we find that in 75% of simulations the outbreak is delayed by at least 11 days (97.5% of simulations: at least 7 days). The possible delay decreases rapidly for more travellers, lower effectiveness of sensitisation, higher R 0 or lower heterogeneity thereof. However, syndromic traveller screening at departure and/or arrival can further enhance impact. In combination with sensitisation, syndromic screening can delay an outbreak substantially longer. In 75% of simulations we find an outbreak delay of at least 111 days (97.5% of simulations: at least 23 days) for 1 infected . CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) traveller per week and at least 9 days (97.5% of simulations: at least 4 days) for 10 infected travellers per week. Limitations include: • We assume a constant rate of infected travellers. However, this may increase rapidly as the epidemic continues to spread exponentially in China and potentially elsewhere. There is currently little evidence for an exponential increase in infected travellers to Europe as airports in the highest risk regions have shut. If indeed infected traveller numbers were to increase exponentially numbers would increase from 1 to 10 and 100 per week within about 19 and 38 days respectively (assuming R=2.5 and serial interval of 7.5) and estimated delays would decrease accordingly. • The only estimate from the current outbreak for the variation between individuals in the number of secondary cases (k) is including large confidence intervals that span estimates for SARS and seasonal influenza. The estimated delay of an outbreak was highly sensitive to k. We assume that syndromic surveillance at entry leads to immediate case isolation and hence no onward transmission. This is ignoring that during the flight the index case may have infected other travellers. We assume that only sensitised travellers would pick up quickly on relevant symptoms and self-isolate and report to trigger contact tracing. Non sensitised travellers are assumed to not pay attention to early influenza-like symptoms during the winter season and hence only report with severe symptoms, i.e. when most of secondary cases have been infected and themselves have potentially further spread the virus. This may overestimate the estimated impact of sensitisation. • We don't explicitly account for potential asymptomatic transmission. However, we implicitly do so as both the syndromic screening as well as the contact tracing work that infomed our estimates accounted for a small proportion of asymptomatic transmitters. Objectives: To determine if interventions aimed at air travellers can delay establishment of a SARS-CoV-2 outbreak in a previously unaffected country. Design: Simulation study Setting: Countries with no sustained SARS-CoV-2 transmission and with no shared border with affected regions Participants: Infected air travellers Interventions: Syndromic screening at departure
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